TCR Mimic Monoclonal Antibodies Induce Apoptosis of Tumor Cells via Immune Effector-Independent Mechanisms

Abstract

mAbs that recognize peptides presented on the cell surface by MHC class I molecules are potential therapeutic agents for cancer therapy. We have previously demonstrated that these Abs, which we termed TCR mimic mAbs (TCRm), reduce tumor growth in models of breast carcinoma. However, mechanisms of TCRm-mediated tumor growth reduction remain largely unknown. In this study, we report that these Abs, in contrast to several mAbs used currently in the clinic, destroy tumor cells independently of immune effector mechanisms such as Ab-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). We found that TCRm-mediated apoptosis of tumor cells was associated with selective and specific binding of these Abs to peptide/HLA class I complexes, which triggered the activation of JNK and intrinsic caspase pathways. This signaling was accompanied by the release of mitochondrial cytochrome c and apoptosis-inducing factor. TCRm-induced apoptosis in tumor cells was completely inhibited by soluble MHC tetramers loaded with relevant peptide as well as with inhibitors for JNK and caspases. Furthermore, mAbs targeting MHC class I, independent of the peptide bound by HLA, did not stimulate apoptosis, suggesting that the Ab-binding site on the MHC/peptide complex determines cytotoxicity. This study suggests the existence of mechanisms, in addition to ADCC and CDC, through which these therapeutic Abs destroy tumor cells. These mechanisms would appear to be of particular importance in severely immunocompromised patients with advanced neoplastic disease, since immune cell-mediated killing of tumor cells through ADCC and CDC is substantially limited in these individuals.

An HLA-Presented Fragment of Macrophage Migration Inhibitory Factor Is a Therapeutic Target for Invasive Breast Cancer

“…When the more aggressive BT-20-A2 tumor was tested in this same model, RL21A administration yielded a .2-fold tumor reduction. This magnitude of tumor reduction is consistent with the previously reported in vivo anti-tumor activity of a TCRm directed toward a p68 peptide/HLA-A2 complex (35,43). The promising in vivo tumor reduction achieved through the targeting of HLA/peptide complexes with TCRm demonstrates that the HLA of cancerous tissues may offer a rich horizon of new complexes that can be successfully targeted by TCRm mAb.…”

“…We have recently demonstrated that TCRm directly activates caspases, apoptosis, and cell death by signaling through specific MHC/peptide complexes (35), and we suspect that RL21A induced in vivo killing of BT-20-A2 tumors by the same mechanism. Indeed, Verma et al (35) showed immune effector-independent anti-tumor mechanisms in vivo using F(ab9) 2 fragments of a different TCRm in the same BT-20-A2 tumor model. Those findings and the modest ADCC and CDC activity observed in vitro for RL21A against BT-20-A2 tumor cells in the current study may point to a CDC-and ADCC-independent mechanism of action for RL21A in vivo.…”

“…TCRm mAbs to HLA/peptide complexes have been shown to directly kill tumor cells through the induction of tumor cell apoptosis (35). In this study, we investigated the ability of RL21A to mediate tumor cell death via the direct induction of apoptosis.…”

Therapeutic antibodies to intracellular targets in cancer therapy

“…As immunotoxin conjugates, these constructs have shown activity against breast and prostate cancer, and melanoma xenografts in mice. Mouse IgG2a mAbs specific for human chorionic gonadotropin (h-CG)-b, p68 RNA helicase and Her2 peptides presented by HLA-A0201 are also active in vivo [10]. Several mechanisms of action were observed in vitro, including ADCC, and surprisingly, CMC (which normally requires high antigen density) and direct induction of apoptosis through the JNK signaling pathway.…”

Detection of Human Leukocyte Antigen Biomarkers in Breast Cancer Utilizing Label-free Biosensor Technology

“…However, the immune system exerts pressure which often promotes selection for viruses or tumor capable of evading an effective CTL response. T-cell receptor mimicking (TCRm) monoclonal antibodies (mAbs) which recognize specific peptide/HLA-A*02:01 complexes such as those derived from breast cancer associated proteins, macrophage migration inhibitory factor (MIF [19][20][21][22][23][24][25][26][27] ) 3 and NY-ESO-1 157-165 , enable detection and destruction of breast cancer cells in the absence of an effective anti-tumor CTL response 4,5 . This representative work is focused on the HLA-A*0201 molecule, which is expressed by up to 30% of the population.…”